Measuring Voltage

ABSTRACT

In one embodiment, a method includes, at a first input of a comparator, receiving from an analog multiplexer one of multiple first voltages. Each of the first voltages results at least in part from an interaction between an object and an electrode of each of one or more nodes of a capacitive touch sensor. The method includes, at a second input of the comparator, receiving a second voltage across a measurement capacitor that has a first terminal coupled to the second input of the comparator. The method includes charging the measurement capacitor at least in part through a measurement resistor coupled in series to the first terminal of the measurement capacitor and monitoring an output of the comparator during the charging of the measurement capacitor. The output of the comparator changes state when the second voltage becomes approximately equal to or greater than the one of the first voltages. The method includes determining an amount of time from a start of the charging of the measurement capacitor to a change in state of the output of the comparator.

TECHNICAL FIELD

This disclosure generally relates to measuring voltage.

BACKGROUND

An array of conductive drive and sense electrodes may form amutual-capacitance touch sensor having one or more capacitive nodes. Themutual-capacitance touch sensor may have either a two-layerconfiguration or single-layer configuration. In the two-layerconfiguration, drive electrodes may be disposed in a pattern on one sideof a dielectric substrate and sense electrodes disposed in a pattern onanother side of the substrate. An intersection of a drive electrode anda sense electrodes in the array may form a capacitive node. At theintersection, the drive and sense electrodes may come near each other,but they do not make electrical contact with each other. Instead, thesense electrode is capacitively coupled to the drive electrode. In thesingle-layer configuration, drive and sense electrodes may be disposedin a pattern on one side of a substrate. In such a configuration, a pairof drive and sense electrodes capacitively coupled to each other acrossa space or dielectric between electrodes may form a capacitive node.

A pulsed or, in some cases, alternating voltage applied to the driveelectrode may induce a charge on the sense electrode, and the amount ofcharge induced may be susceptible to external influence (such as a touchby or the proximity of an object). When an object, separated from driveand sense electrodes by a dielectric layer, comes within proximity ofthe drive and sense electrodes, a change in capacitance may occur atthat capacitive node and a controller may measure the change incapacitance as a change in voltage. By measuring voltages throughout thearray and applying an algorithm to the measured signal, the controllermay determine the position of the touch or proximity on the touchsensor.

In a single-layer configuration for a self-capacitance implementation,an array of vertical and horizontal conductive electrodes of only asingle type (e.g. drive) may be disposed in a pattern on one side of thesubstrate. Each of the conductive electrodes in the array may form acapacitive node, and, when an object touches or comes within proximityof the electrode, a change in self-capacitance may occur at thatcapacitive node and a controller may measure the change in capacitanceas a change in voltage or a change in the amount of charge needed toraise the voltage to some pre-determined amount. As with amutual-capacitance touch screen, by measuring voltages throughout thearray, the controller may determine the position of the touch orproximity on the touch sensor.

In a touch-sensitive display application, a touch screen may enable auser to interact directly with what is displayed on a display underneaththe touch screen, rather than indirectly with a mouse or touchpad. Atouch screen may be attached to or provided as part of, for example, adesktop computer, laptop computer, tablet computer, personal digitalassistant (PDA), smartphone, satellite navigation device, portable mediaplayer, portable game console, kiosk computer, point-of-sale device, orother suitable device. A control panel on a household or other appliancemay include a touch screen.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example system for measuring voltage.

FIG. 2 illustrates an example use of the example system of FIG. 1 with amutual-capacitance touch sensor.

FIG. 3 illustrates an example use of the example system of FIG. 1 with aself-capacitance touch sensor.

FIG. 4A illustrates an example system for measuring voltage usingcapacitive charging through a single capacitor.

FIG. 4B illustrates an example system for measuring voltage usingcapacitive charging through multiple capacitors.

FIG. 5 illustrates example voltage across the measurement capacitor inthe example system of FIG. 4A over time.

FIG. 6 illustrates an example system for measuring voltage usingadaptive charge cancellation.

FIG. 7 illustrates example voltage across the measurement capacitor inthe example system of FIG. 6 over time.

FIG. 8A illustrates an example system for measuring voltage usingresistive charging through a single additional resistor.

FIG. 8B illustrates an example system for measuring voltage usingresistive charging through multiple resistors.

FIG. 9 illustrates example voltage across the measurement capacitor inthe example system of FIG. 8A over time.

FIG. 10A illustrates an example system for measuring voltage usingresistive and capacitive charging through a single resistor andcapacitor.

FIG. 10B illustrates an example system for measuring voltage usingresistive and capacitive charging through multiple resistors andcapacitors.

FIG. 11 illustrates example voltage across the measurement capacitancein the example system of FIG. 10A over time.

FIG. 12 illustrates an example system for measuring voltage usingresistive and capacitive charging through a parallel resistor andcapacitor.

FIG. 13 illustrates an example method for measuring voltage.

DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 illustrates an example system 100 for measuring voltage. In theexample of FIG. 1, system 100 includes a controller 102 with an analogmultiplexer 104 and a comparator 106. Controller 102 is coupled to oneor more sense lines Y0-Yn, one or more sampling capacitors CS0-CSn, ameasurement resistor RM, and a measurement capacitor CM. Each ofsampling capacitors CS0-CSn has a terminal coupled to a correspondingone of sense lines Y0-Yn and another terminal coupled to a correspondingone of inputs M0-Mn to analog multiplexer 104. The output of analogmultiplexer 104 is coupled to one of the inputs of comparator 102, and aterminal of measurement capacitor CM is coupled through terminal REF toanother one of the inputs to comparator 106. That same terminal ofmeasurement capacitor CM is also coupled through measurement resistor RMto terminal MEAS of controller 102. The other terminal of measurementcapacitor CM is coupled to ground. Although this disclosure describesand illustrates a particular arrangement of particular components forsystem 100, this disclosure contemplates any suitable arrangement of anysuitable components for system 100.

Controller 102 may be coupled to a touch sensor through one or moresense lines Y0-Yn. In particular embodiments, the touch sensor may be amutual-capacitance touch sensor that includes an array of driveelectrodes and sense electrodes coupled to one of corresponding drivelines and sense lines Y0-Yn, respectively. Each intersection of a driveelectrode and sense electrode forms a capacitive node. In otherparticular embodiments, the touch sensor may be a self-capacitance touchsensor. The self-capacitance touch sensor includes one or moreelectrodes in horizontal and vertical directions, where each electrodemay be coupled to one of corresponding sense line Y0-Yn (otherwisereferred to as SNS or SNSK in self-capacitance touch sensorapplications). Self-capacitance touch sensor detects a presence of anobject as an interaction between an object (not shown) and an electricfield generated by one or more electrodes of self-capacitance touchsensor. Although this disclosure describes a particular controllerhaving particular functionality with respect to particular touchsensors, this disclosure contemplates any suitable controller having anysuitable functionality with respect to any suitable application withoutuse of touch sensors.

Controller 102 may detect and process a change in capacitance todetermine the presence and location of a touch or proximity input.Controller 102 may then communicate information about the touch,detecting a touch position without surface contact (“hovering”), orproximity input to one or more other components (such one or morecentral processing units (CPUs) or digital signal processors (DSPs)) ofa device, which may respond to the touch or proximity input byinitiating a function of the device (or an application running on thedevice) associated with it. Controller 102 may be one or more integratedcircuits (ICs), such as for example general-purpose microprocessors,microcontrollers, programmable logic devices or arrays,application-specific ICs (ASICs). Although this disclosure describes andillustrates a particular controller in the device, this disclosurecontemplates any suitable controller in the device.

Sense lines Y0-Yn are configured to communicate one or more voltages toinputs M0-Mn of analog multiplexer 104. The analog multiplexer 104selects one of the voltages from sense lines Y0-Yn stored acrosssampling capacitors CS0-CSn and transmits the selected voltage to one ofthe inputs of comparator 106 for comparison with the voltage acrossmeasurement capacitor CM, as discussed below. In particular embodiments,analog multiplexer 104 selects the voltage across each samplingcapacitor CS0-CSn in accordance with a predetermined sequence.

As discussed above, comparator 106 compares the voltage acrossmeasurement capacitor CM to the voltage across selected one of samplingcapacitors CS0-CSn. The voltage across the measurement capacitor CM isincreased by providing charge through measurement resistor RM. Chargingof measurement capacitor CM may be initiated by coupling measurementresistor RM to terminal MEAS of controller 102. In particularembodiments, terminal MEAS is configured to alternatively provide groundor a supply voltage. Since the supply voltage, resistance of measurementresistor RM, and capacitance of measurement capacitor CM are constant,the voltage across measurement capacitor CM is a function of time.

The output of comparator 106 is monitored during charging of measurementcapacitor CM. When the voltage across measurement capacitor CM issubstantially equal or greater than the voltage across the selected oneof sampling capacitors CS0-CSn, the output of the comparator 106 changesstate. The voltage across selected one of sampling capacitors CS0-CSn,or a value proportional to the voltage, may be determined from an amountof time elapsed from a start of charging measurement capacitor CM untilthe change in state of the output of comparator 106. After determiningthe amount of time from the start of the charging of the measurementcapacitor CM until a change in state of the output of the comparator106, measurement capacitor CM may be discharged in preparation forsubsequent voltage measurement. The amount of time may be thendetermined for the voltage across another one of sampling capacitorsCS0-CSn.

FIG. 2 illustrates an example use of the example system 100 of FIG. 1with a mutual-capacitance touch screen 108. As illustrated in theexample of FIG. 2, example system 100 of FIG. 1 may be furtherconfigured to measure voltages from mutual-capacitance touch screen 108.In particular embodiments, controller 102 includes a driver 110 coupledto one or more drive lines X0-Xm. Mutual-capacitance touch screen 108includes an array of drive electrodes and sense electrodes coupled toone of corresponding drive lines X0-Xm and sense lines Y0-Yn,respectively. Each intersection of a drive electrode (electrode_(i)) andsense electrode (electrode_(j)) forms a capacitive nodeC_(x00)-C_(xnm)(C_(ji)(i=0 . . . n, j=0 . . . m)).

Driver 110 transmits a drive signal to one or more columns of driveelectrodes through drive lines X0-Xm. The drive signal induces charge onthe associated sense electrode through capacitive nodes C_(x00)-C_(xnm).Interaction between an object (not shown) and mutual-capacitance touchscreen 108 may affect the amount of charge induced on one or more senseelectrodes. The induced charge may be transferred from the senseelectrodes to sampling capacitors CS0-CSn through sense lines Y0-Yn andstored as a voltage across sampling capacitors CS0-CSn, as discussedabove. In particular embodiments, charge may be accumulated on senseelectrodes through bursts of two or more charge transfers.

TABLE 1 illustrates an example sequence of operations for measuringvoltage from mutual-capacitance touch sensor 108. Steps 1-10 transfercharge induced on the sense electrode to corresponding samplingcapacitor CS0-CSn. In particular embodiments, steps 1-9 are performed anumber of times corresponding to a burst length associated with themutual-capacitance touch sensor 108. Steps 11-15 measures voltage acrosseach sampling capacitors CS0-CSn by measuring the amount of time elapsedfrom the start of charging measurement capacitor CM until the voltageacross measurement capacitor CM through terminal REF is substantiallyequal or higher than the voltage across the selected one of samplingcapacitors CS0-CSn, as discussed above. In particular embodiments, step14 performs steps 11-13 for each column of drive electrodes. Althoughthis disclosure describes and illustrates a particular sequence of stepsin TABLE 1, this disclosure contemplates any suitable sequence of stepsin system 100 for measuring voltages.

TABLE 1 Step X Y M REF MEAS Description 1 0 0 0 0 0 Initial dischargestate - all capacitors will be fully discharged 2 1 0 0 0 0 Prepare thedrive lines X0-Xm for charge transfer 3 1 0 F 0 0 Float multiplexerinputs M0-Mn 4 1 F F 0 0 Float sense lines Y0-Yn 5 1 F 0 0 0 Couplemultiplexer inputs M0-Mn to ground 6 0 F 0 0 0 Charge transfer tosampling capacitors CS0-CSn 7 0 F F 0 0 End of charge transfer 8 0 0 F 00 Provide ground to sense lines Y0-Yn 9 1 F F 0 0 Return selected driveline X0-Xm to the high state and prepare for new transfer 10 Repeatoperations 4-9 N times 11 0 0 F 0 0 Couple comparator 106 to multiplexer104 and terminal REF. Select multiplexer input M0-Mn. Connect senselines Y0-Yn to ground and set drive lines X0-Xm to ground 12 0 0 F F 1Start charging CM by coupling RM to power supply. Start measuring thetime until the state of the output of comparator 102 changes 13 0 0 F 00 Discharge measurement capacitor CM through the comparator 102 inputand terminals REF and MEAS 14 Repeat operations 11-13 for each lineY0-Yn 15 0 0 0 0 0 Discharge sampling capacitors CS0-CSn, repeat foractive drive lines X0-Xm 16 0 0 0 0 0 Discharge all capacitors F =floating, i.e., high-impedance state 0 = logic low 1 = logic high

FIG. 3 illustrates an example use of the example system of FIG. 1 with aself-capacitance touch sensor 112. As discussed above, self-capacitancetouch sensor 112 includes one or more electrodes coupled tocorresponding one of sense lines Y0-Yn. An interaction between an objectand an electric field generated by one or more horizontal and verticalelectrodes of self-capacitance touch sensor 112 is measured as a voltagestored on sampling capacitors CS0-CSn. The voltage results from adifference in capacitance formed between the object and the electrodecompared to a free space capacitance of the electrode. As discussedabove, voltages across sampling capacitors CS0-CSn are measured from theamount of time from the start of charging measurement capacitor CM untilthe voltage across measurement capacitor CM through terminal REF issubstantially equal or higher than the voltage across the selected oneof sampling capacitors CS0-CSn. In particular embodiments, measuringvoltages from self-capacitance touch sensor 112 may be performed usingoperations 11-13 of TABLE 1 discussed above.

FIG. 4A illustrates an example system for measuring voltage usingcapacitive charging through a single capacitor. In practical terms, therate in which the operations of TABLE 1 may be performed may be limitedby the amount of time elapsed between the start of charging measurementcapacitor CM until the voltage across measurement capacitor CM issubstantially equal or higher than the voltage across the selected oneof sampling capacitors CS0-CSn. Reducing the amount of time required tochange the state of the comparator 106 increases the rate in whichmeasuring voltages across sampling capacitors CS0-CSn may be performed.

As illustrated in the example of FIG. 4A, a predetermined amount ofcharge may be transferred from an additional capacitor CZ coupled inseries with the measurement capacitor CM prior to resistive chargingthrough measurement resistor RM. As discussed above, the voltage acrossselected one of sampling capacitors CS0-CSn may be transmitted tocomparator 106 through corresponding input M0-Mn of multiplexer 104.Providing the supply voltage to terminal MEAS initiates charging of themeasurement capacitor CM and forms a capacitive voltage divider withcapacitor CZ and measurement capacitor CM. Resistive charging ofmeasurement capacitor CM through measurement resistor RM predominatesthe charging process after capacitive charging from capacitor CZ. Inother particular embodiments, the capacitance of capacitor CZ is smallerthan the capacitance of measurement capacitor CM.

FIG. 4B illustrates an example system for measuring voltage usingcapacitive charging through multiple capacitors. As illustrated in theexample of FIG. 4B, an amount of charge may be transferred from eachadditional capacitor C1 z-Cnz coupled in series with the measurementcapacitor CM prior to resistive charging through measurement resistorRM. As discussed above, the voltage across selected one of samplingcapacitors CS0-CSn is transmitted to comparator 106 throughcorresponding input M0-Mn of multiplexer 104. Charging of themeasurement capacitor CM may be performed by providing a voltage fromone of terminals CANCEL1-CANCELn coupled to a terminal of capacitors C1z-Cnz. Each capacitor C1 z-Cnz in turn transfers charge to measurementcapacitor CM. The amount of charge transferred by each depending on therelative capacitance of each additional capacitor C1 z-Cnz tomeasurement capacitor CM. As discussed above, resistive charging ofmeasurement capacitor CM through measurement resistor RM predominatesthe charging process after charge transfers from capacitors C1 z-Cnz.

FIG. 5 illustrates example voltage across the measurement capacitor inthe example system of FIG. 4A over time. As illustrated in the exampleof FIG. 5, initial charging of the measurement capacitor ispredominantly from charge transfer through the additional capacitor CZcoupled in series with the measurement capacitor. The amount of chargetransferred from additional capacitor CZ, as well as voltage 110 atterminal REF, may be determined from supply voltage applied to thecapacitor CZ, as well as the relative values of CZ and CM. As discussedabove, after the charge transfer, further charging of the measurementcapacitor beyond voltage 110 arises predominantly from resistivecharging through the measurement resistor. The rate of increase in thevoltage across the measurement capacitor may be determined by theresistance of the measurement resistor. As illustrated by the example ofFIG. 5, the addition of capacitive charging to resistive charging of themeasurement capacitor achieves a reduction of elapsed voltagemeasurement time compared to resistive charging alone.

FIG. 6 illustrates an example system for measuring voltage usingadaptive charge cancellation. As illustrated in the example of FIG. 6,controller 102 may be configured in a similar fashion to the system ofFIG. 4A, except of measurement capacitor CM may be coupled betweenterminal REF and terminal CLAMP. In particular embodiments, terminalCLAMP may be configured to alternately provide either ground or ahigh-impedance state, e.g., float, to one terminal of measurementcapacitor CM. For each charging cycle, an amount of charge will betransferred from additional capacitor CZ to the measurement capacitorCM, as discussed below.

TABLE 2 illustrates an example sequence of operations for measuringvoltage using adaptive charge cancellation. Steps 1-10 (not shown)transfer charge induced on the sense electrode to the associatedsampling capacitor CS0-CSn, as discussed in TABLE 1. Steps 11-20 measurevoltage across one of sampling capacitors CS0-CSn by measuring theamount of time elapsed for a state of an output of the comparator 106 tochange. In particular embodiments, step 20 performs step 11-19 forpredetermined number of charge transfers. In other particularembodiments, the predetermined number of charge transfers may be equalto a burst length of a touch sensor. Steps 21-22 measure voltage acrossselected one of sampling capacitors CS0-CSn by measuring the amount oftime elapsed from the start of charging measurement capacitor CM untilthe voltage across measurement capacitor CM through terminal REF issubstantially equal or higher than the voltage across the selected oneof sampling capacitors CS0-CSn, as discussed above. In other particularembodiments, step 23 performs steps 11-22 for each input M0-Mn ofmultiplexer 104. Although this disclosure describes and illustrates aparticular sequence of steps in TABLE 2, this disclosure contemplatesany suitable sequence of steps in system 100 for measuring voltages.

TABLE 2 Step X Y REF M CLAMP MEAS Description 11 0 0 0 F 0 0 Connectanalog comparator 106 to multiplexer 104 and terminal MEAS. Select aninput M0-Mn of multiplexer 104. Connect sense lines Y0-Yn to GND, setdrive lines X0-Xn to GND 12 0 0 F F 0 1 Make charge transfer between Czand CM. 13 0 0 F F 0 F End of the charge transfer between Cz and CM 14 00 F F F F Float CLAMP terminal 15 0 0 1 F F F Connect M to Vcc andprepare for discharging of Cz 16 0 0 1 F F 1 Discharge Cz by settingterminal MEAS and REF to Vcc 17 0 0 1 F F F End of Cz discharging 18 0 0F F F F Float selected multiplexer input M0-Mn 19 0 0 F F 0 F Preparefor the next charge transfer 20 Loop between Cz & CM - Go To Step 12 Ntimes to generate the voltage on CM 21 0 0 F F 0 1 Start measuring thevoltage on multiplexer input M0-Mn by charging CM through RM - measurethe time until the comparator 106 output changes state 22 0 0 0 0 0Discharging measurement capacitor CM through the comparator 106 inputand terminals REF and CLAMP 23 Loop - Go To Step 11 for each multiplexerinput M0-Mn 24 0 0 0 0 Discharge all capacitors F = floating, i.e.,high-impedance state 0 = logic low 1 = logic high

FIG. 7 illustrates example voltage across the measurement capacitor inthe example system of FIG. 6 over time. As illustrated in the example ofFIG. 7, initial charging of the measurement capacitor is predominantlythrough multiple charge transfers through additional capacitor CZcoupled in series with the measurement capacitor. After each chargetransfer from capacitor CZ, the incremental increase in the voltage atterminal REF may be determined by the supply voltage transmitted byterminal MEAS and the relative capacitances of capacitor CZ and themeasurement capacitor. After predetermined number of charge transfers,further charging of the measurement capacitor from voltage 120 arisespredominantly from resistive charging through the measurement resistor.As illustrated by the example of FIG. 7, capacitive charging throughadaptive charge cancellation in addition to resistive charging of themeasurement capacitor achieves a reduction of elapsed time for thevoltage of terminal REF to substantially equal the voltage of selectedsampling capacitor over resistive charging alone.

FIG. 8A illustrates an example system for measuring voltage usingresistive charging through a single additional resistor. As illustratedin the example of FIG. 8A, example system 100 of FIG. 1 may beconfigured for resistive charging using an additional resistor RFcoupled in series with measurement capacitor CM. Charge may be injectedto measurement capacitor CM at a different rate, i.e., current, usingadditional resistor RF compared to resistive charging entirely throughmeasurement resistor RM. In particular embodiments, the resistance ofresistor RF is smaller than the resistance of measurement resistor RM.

TABLE 3 illustrates an example sequence of operations for measuringvoltage using resistive charging using a single resistor. A voltage,e.g., a power supply voltage, for injecting charge to the measurementcapacitor CM is transmitted to resistor RF by controller 102 throughterminal FAST. Steps 1-10 (not shown) transfer charge induced on thesense electrode to the associated sampling capacitor CS0-CSn, asdiscussed in TABLE 1. Steps 11-16 measure voltages across samplingcapacitors CS0-CSn by measuring the amount of time elapsed for a stateof output of the comparator 106 to change. Steps 12-13 measure voltageacross the selected one of sampling capacitors CS0-CSn by measuring theamount of time elapsed from the start of charging measurement capacitorCM until the voltage across measurement capacitor CM through terminalREF is equal or higher than the voltage across the selected one ofsampling capacitors CS0-CSn, as discussed above. Step 12 initiatescharging of the measurement capacitor CM by transmitting a voltage toterminal MEAS and FAST. Step 13 discontinues resistive charging throughresistor RF and at this time, resistive charging through measurementresistor RM predominates charging of measurement capacitor CM. Inparticular embodiments, step 14 performs steps 11-13 for each inputM0-Mn of multiplexer 104. Although this disclosure describes andillustrates a particular sequence of steps in TABLE 3, this disclosurecontemplates any suitable sequence of steps in system 100 for measuringvoltages.

TABLE 3 Step X Y M FAST MEAS Description 11 0 0 F 0 0 Connect analogcomparator 106 to multiplexer 104 and terminal REF. Select desired inputM0-Mn of the multiplexer. Connect sense lines Y0-Yn to GND, set drivelines to GND 12 0 0 F 1 1 Start measuring the voltage on selectedmultiplexer input M0-Mn by charging CM through RM and RF. 13 0 0 F F 1Float FAST terminal - end of the fast charging. Measure with the timeuntil the comparator 106 flips 14 0 0 F 0 0 Discharging samplingcapacitor CM through the comparator 106 input and terminals MEAS andFAST 15 Loop - Go To Step 11 for each multiplexer input M0- Mn 16 0 0 00 Discharge all capacitors F = floating, i.e., high-impedance state 0 =logic low 1 = logic high

FIG. 8B illustrates an example system for measuring voltage usingresistive charging through multiple resistors. As illustrated in theexample of FIG. 8B, example system 100 of FIG. 8A may be configured forresistive charge using multiple resistors RF0-RFn coupled in series withmeasurement capacitor CM. Resistive charging of the measurementcapacitor CM may be performed by providing a voltage from one ofterminals FAST11-FASTn coupled to a terminal of resistors RF0-RFn. Asdiscussed above, charge may be injected to measurement capacitor CM atdifferent rates using additional resistors RF0-RFn compared to resistivecharging entirely through measurement resistor RM. In particularembodiments, the resistance of each resistor RF0-RFn is smaller than theresistance of measurement resistor RM. A voltage, e.g., a power supplyvoltage, for injecting charge to the measurement capacitor CM istransmitted to resistors RF0-RFn by controller 102 through correspondingterminals FAST0-FASTn. In particular embodiments, the application ofvoltage to each resistor RF0-RFn is discontinued in a sequence based onthe voltage across the measurement capacitor CM measured at terminalREF.

FIG. 9 illustrates example voltage across the measurement capacitor inthe example system of FIG. 8A over time. As illustrated in the exampleof FIG. 9, initial charging of the measurement capacitor ispredominantly from charge injected to the measurement capacitor throughadditional resistor RF coupled in series with the measurement capacitor.The rate in which charge is injected to the measurement capacitorthrough resistor RF, i.e., current, may be determined from supplyvoltage applied to resistor RF, as well as the resistance of resistorRF. As discussed above, after the charge injection through resistor RF,further charging of the measurement capacitor from voltage 130 arisespredominantly from resistive charging through the measurement resistor.The rate of increase in the voltage across the measurement capacitor maybe determined by the resistance of the measurement resistor and resistorRF. As illustrated by the example of FIG. 9, resistive charging througha combination of the measurement resistor and resistor RF achieves areduction of elapsed voltage measurement time compared to resistivecharging through the measurement resistor alone.

FIG. 10A illustrates an example system for measuring voltage usingresistive and capacitive charging through a single resistor andcapacitor. As illustrated in the example of FIG. 10A, example system 100of FIG. 1 may be configured for a combination of resistive andcapacitive charging using additional resistor RF and capacitor Czcoupled in series with measurement capacitor CM. As discussed in FIG.8A, charge may be injected to measurement capacitor CM at a differentrate, i.e., current by using additional resistor RF compared toresistive charging entirely through measurement resistor RM. Inaddition, as discussed in FIG. 4A, a predetermined amount of charge maybe transferred from additional capacitor Cz coupled in series with themeasurement capacitor CM prior to resistive charging through measurementresistor RM. In particular embodiments, the resistance of resistor RF issmaller than the resistance of measurement resistor RM and thecapacitance of capacitor Cz is smaller than the capacitance ofmeasurement capacitor CM.

FIG. 10B illustrates an example system for measuring voltage usingresistive and capacitive charging through multiple resistors andcapacitors. As illustrated in the example of FIG. 10B, example system100 of FIG. 10A may be configured for resistive and capacitive chargingusing multiple resistors RF0-RFn and capacitors C1 z-Cnz coupled inseries with measurement capacitor CM. As discussed in FIG. 4A, chargemay be injected to measurement capacitor CM at different rates usingadditional resistors RF0-RFn compared to resistive charging entirelythrough measurement resistor RM. Resistive charging of the measurementcapacitor CM may be performed by providing a voltage from one ofterminals FAST11-FASTn coupled to a terminal of resistors RF0-RFn. Inparticular embodiments, the application of voltage to each resistorRF0-RFn is discontinued in a sequence based on the voltage across themeasurement capacitor CM measured at terminal REF.

As discussed in FIG. 4B, capacitive charging of the measurementcapacitor CM may be performed by providing a voltage from one ofterminals CANCEL1-CANCELn coupled to a terminal of capacitors C1 z-Cnz.Each capacitor C1 z-Cnz in turn transfers charge to measurementcapacitor CM. The amount of charge transferred by each capacitor C1z-Cnz depends on the relative capacitance of each additional capacitorC1 z-Cnz to measurement capacitor CM.

FIG. 11 illustrates example voltage across the measurement capacitancein the example system of FIG. 10A over time. As illustrated in theexample of FIG. 11, charging of the measurement capacitor may beanalyzed in three stages. One stage charges the measurement capacitorpredominantly from charge transfer through additional capacitor CZcoupled in series with the measurement capacitor to voltage 110. Asdiscussed in FIG. 5, the amount of charge transferred from additionalcapacitor CZ may be determined from supply voltage applied to thecapacitor CZ, as well as the relative values of capacitor CZ and themeasurement capacitor.

Another stage charges the measurement capacitor predominantly fromcharge injected to the measurement capacitor through additional resistorRF coupled in series with the measurement capacitor. The rate in whichcharge is injected to the measurement capacitor through resistor RF maybe determined from the supply voltage applied to resistor RF, as well asthe resistance of resistor RF. Another stage charges the measurementcapacitor from voltage 130 predominantly from resistive charging throughthe measurement resistor. As illustrated by the example of FIG. 11,resistive charging through a combination of the capacitive chargingthrough capacitor CZ and resistive charging through measurement resistorand resistor RF achieves a reduction of elapsed voltage measurement timecompared to resistive charging through the measurement resistor alone.

FIG. 12 illustrates an example system for measuring voltage usingresistive and capacitive charging through a parallel resistor andcapacitor. In particular embodiments, a parallel combination ofadditional resistor RF and additional capacitor Cz may be coupled inseries with measurement capacitor CM. During charging of measurementcapacitor CM, noise from a power supply (not shown) may be introducedinto system 100 through capacitor Cz. After resistive charging throughadditional resistor RE, additional capacitor Cz may be decoupled fromthe power supply. Decoupling additional capacitor Cz from the powersupply shields voltage measurement by system 100 from power supplynoise.

FIG. 13 illustrates an example method for measuring voltage. The methodmay start at operation 200, an example system receives one of a firstvoltage. In particular embodiments, each first voltage may be stored asa voltage across one of sense capacitors. At operation 202, examplesystem charges a measurement capacitor. In particular embodiments, themeasurement capacitor may be charged by resistive charging through anadditional resistor coupled in series to the measurement capacitor. Inother particular embodiments, the measurement capacitor may be chargedby capacitive charging through an additional capacitor coupled in seriesto the measurement capacitor. Operation 204 monitors output of acomparator during charging of the measurement capacitor. In particularembodiments, the comparator output may be based on the first voltagestored across one of sense capacitors and a second voltage stored acrossthe measurement capacitor, as illustrated in FIG. 1. Depending on theinput configuration of the comparator, the output of the comparator maychange state when the second voltage becomes approximately equal orgreater than the first voltage stored across one of sense capacitors. Atoperation 206, an amount of time from a start of charging themeasurement capacitor through the measurement resistor until when thechange of state of the comparator output is determined, at which pointthe method may end. Although this disclosure describes and illustratesparticular operations of the method of FIG. 13 as occurring in aparticular order, this disclosure contemplates any suitable operationsof the method of FIG. 13 occurring in any suitable order. Moreover,although this disclosure describes and illustrates particular componentscarrying out particular steps of the method of FIG. 13, this disclosurecontemplates any suitable combination of any suitable componentscarrying out any suitable operations of the method of FIG. 13.

Herein, reference to a computer-readable storage medium encompasses oneor more non-transitory, tangible computer-readable storage mediapossessing structure. As an example and not by way of limitation, acomputer-readable storage medium may include a semiconductor-based orother integrated circuit (IC) (such, as for example, afield-programmable gate array (FPGA) or an application-specific IC(ASIC)), a hard disk, an HDD, a hybrid hard drive (HHD), an opticaldisc, an optical disc drive (ODD), a magneto-optical disc, amagneto-optical drive, a floppy disk, a floppy disk drive (FDD),magnetic tape, a holographic storage medium, a solid-state drive (SSD),a RAM-drive, a SECURE DIGITAL card, a SECURE DIGITAL drive, or anothersuitable computer-readable storage medium or a combination of two ormore of these, where appropriate. Herein, reference to acomputer-readable storage medium excludes any medium that is noteligible for patent protection under 35 U.S.C. §101. Herein, referenceto a computer-readable storage medium excludes transitory forms ofsignal transmission (such as a propagating electrical or electromagneticsignal per se) to the extent that they are not eligible for patentprotection under 35 U.S.C. §101. A computer-readable non-transitorystorage medium may be volatile, non-volatile, or a combination ofvolatile and non-volatile, where appropriate.

Herein, “or” is inclusive and not exclusive, unless expressly indicatedotherwise or indicated otherwise by context. Therefore, herein, “A or B”means “A, B, or both,” unless expressly indicated otherwise or indicatedotherwise by context. Moreover, “and” is both joint and several, unlessexpressly indicated otherwise or indicated otherwise by context.Therefore, herein, “A and B” means “A and B, jointly or severally,”unless expressly indicated otherwise or indicated otherwise by context.

This disclosure encompasses all changes, substitutions, variations,alterations, and modifications to the example embodiments herein that aperson having ordinary skill in the art would comprehend. Similarly,where appropriate, the appended claims encompass all changes,substitutions, variations, alterations, and modifications to the exampleembodiments herein that a person having ordinary skill in the art wouldcomprehend. Moreover, reference in the appended claims to an apparatusor system or a component of an apparatus or system being adapted to,arranged to, capable of, configured to, enabled to, operable to, oroperative to perform a particular function encompasses that apparatus,system, component, whether or not it or that particular function isactivated, turned on, or unlocked, as long as that apparatus, system, orcomponent is so adapted, arranged, capable, configured, enabled,operable, or operative.

What is claimed is:
 1. A method comprising: at a first input of acomparator, receiving from an analog multiplexer one of a plurality offirst voltages, each of the first voltages resulting at least in partfrom an interaction between an object and an electrode of each of one ormore nodes of a capacitive touch sensor; at a second input of thecomparator, receiving a second voltage across a measurement capacitorthat has a first terminal coupled to the second input of the comparator;charging the measurement capacitor at least in part through ameasurement resistor coupled in series to the first terminal of themeasurement capacitor; monitoring an output of the comparator during thecharging of the measurement capacitor, the output of the comparatorchanging state when the second voltage becomes approximately equal to orgreater than the one of the first voltages; and determining an amount oftime from a start of the charging of the measurement capacitor to achange in state of the output of the comparator.
 2. The method of claim1, wherein one or more additional resistors are coupled in series to thefirst terminal of the measurement capacitor.
 3. The method of claim 1,wherein one or more additional capacitors are coupled in series to thefirst terminal of the measurement capacitor.
 4. The method of claim 1,wherein a second terminal of the measurement capacitor is coupled to aswitch configured to alternate between providing ground and a highimpedance state to the second terminal of the measurement capacitor. 5.The method of claim 1, wherein: one or more additional capacitors arecoupled in series to the first terminal of the measurement capacitor;and one or more additional resistors are coupled in series to the firstterminal of the measurement capacitor.
 6. The method of claim 5, whereinthe one or more additional capacitors are coupled in parallel to the oneor more additional resistors.
 7. The method of claim 1, wherein each ofthe first voltages is across one of a plurality of sampling capacitors,each of the sampling capacitors being coupled to one of a plurality ofinputs of the analog multiplexer.
 8. A circuit configured to: at a firstinput of a comparator, receive from an analog multiplexer one of aplurality of first voltages, each of the first voltages resulting atleast in part from an interaction between an object and an electrode ofeach of one or more nodes of a capacitive touch sensor; at a secondinput of the comparator, receive a second voltage across a measurementcapacitor that has a first terminal coupled to the second input of thecomparator; charge a measurement capacitor at least in part through ameasurement resistor coupled in series to the first terminal of themeasurement capacitor; monitor an output of the comparator during thecharging of the measurement capacitor, the output of the comparatorchanging state when the second voltage becomes approximately equal orgreater than the one of the first voltages; and determine an amount oftime from a start of the charging of the measurement capacitor to achange of state of the output of the comparator.
 9. The circuit of claim8, wherein one or more additional resistors are coupled in series to thefirst terminal of the measurement capacitor.
 10. The circuit of claim 8,wherein one or more additional capacitors are coupled in series to thefirst terminal of the measurement capacitor.
 11. The circuit of claim 8,wherein a second terminal of the measurement capacitor is coupled to aswitch configured to alternate between providing ground and a highimpedance state to the second terminal of the measurement capacitor. 12.The circuit of claim 8, wherein: one or more additional capacitors arecoupled in series to the first terminal of the measurement capacitor;and one or more additional resistors are coupled in series to the firstterminal of the measurement capacitor.
 13. The circuit of claim 8,wherein each of the first voltages is a voltage across one of aplurality of sampling capacitors, each of the sampling capacitors beingcoupled to one of a plurality of inputs of the analog multiplexer, eachof the first voltages resulting at least in part from charge transferbetween a drive electrode and a sense electrode of each of one or morenodes of a capacitive touch sensor.
 14. An apparatus comprising: acapacitive touch sensor that comprises a plurality of inputs of ananalog multiplexer; and one or more computer-readable non-transitorystorage media coupled to the capacitive touch sensor that embody logicthat is operable when executed to: at a first input of a comparator,receive from the analog multiplexer one of a plurality of firstvoltages, each of the first voltages resulting at least in part from aninteraction between an object and a sense electrode of each of one ormore nodes of a capacitive touch sensor; at a second input of thecomparator, receive a second voltage across a measurement capacitor thathas a first terminal coupled to the second input of the comparator;charge a measurement capacitor at least in part through a measurementresistor coupled in series to the first terminal of the measurementcapacitor; monitor an output of the comparator during the charging ofthe measurement capacitor, the output of the comparator changing statewhen the second voltage becomes approximately equal or greater than oneof the first voltages; and determine an amount of time from a start ofthe charging of the measurement capacitor to a change in state of theoutput of the comparator.
 15. The apparatus of claim 14, wherein one ormore additional resistors are coupled in series to the first terminal ofthe measurement capacitor.
 16. The apparatus of claim 14, wherein one ormore additional capacitors are coupled in series to the first terminalof the measurement capacitor.
 17. The apparatus of claim 14, wherein asecond terminal of the measurement capacitor is coupled to a switchconfigured to alternate between providing ground and a high impedancestate to the second terminal of the measurement capacitor.
 18. Theapparatus of claim 14, wherein: one or more additional capacitors arecoupled in series to the first terminal of the measurement capacitor;and one or more additional resistors are coupled in series to the firstterminal of the measurement capacitor.
 19. The apparatus of claim 18,wherein the one or more additional capacitors are coupled in parallel tothe one or more additional resistors.
 20. The apparatus of claim 14,wherein each of the first voltages is a voltage across one of aplurality of sampling capacitors, each of the sampling capacitors beingcoupled to one of the plurality of inputs of the analog multiplexer.